How do you find the exact value of cos (pi)/2?

Related questions

• How do you find the trigonometric functions of any angle?
• What is the reference angle?
• How do you use the ordered pairs on a unit circle to evaluate a trigonometric function of any angle?
• What is the reference angle for #140^\circ#?
• How do you find the value of #cot 300^@#?
• What is the value of #sin -45^@#?
• How do you find the trigonometric functions of values that are greater than #360^@#?
• How do you use the reference angles to find #sin210cos330-tan 135#?
• How do you know if #sin 30 = sin 150#?
• How do you show that #(costheta)(sectheta) = 1# if #theta=pi/4#?